Recently, in connection with techniques for suppressing vibrations of a tower-like structure such as, for example, a high-rise building or a tower of a suspension bridge or a cable-stayed bridge due to the wind or an earthquake, there has been proposed various damping devices based upon the principle of a dynamic vibration damper.
Generally, the principle of the dynamic vibration damper is to absorb the vibrational energy of the structure by providing a natural frequency tuned to a natural frequency of the structure and also by providing a suitable damping mechanism. The principle has been realized in various forms.
A typical form employs the combination of a mass, a spring and a damper. However, such a dynamic damper has the following problems:
(1) It is hard to adjust the natural frequency.
(2) Maintenance is required for aged deterioration of the spring, the damper or the like.
(3) The structural composition and the mechanism are complicated.
(4) Space for accommodating the damping device is limited.
Recently, as one means for solving the above problems, there has been proposed in Japanese Patent Laid-open Publication Nos. 62-101764, 62-292943 and 63-172092 a dynamic vibration damper which utilizes a liquid free surface wave motion (sloshing) within a liquid-filled tank. In accordance with this dynamic vibration damper, the natural frequency of the sloshing is tuned to that of the structure, and the damping mechanism is formed by disposing a porous member or the like within the liquid as an obstacle against the motion of the liquid. However, such a dynamic vibration damper likewise has the following problems:
(1) The sloshing action in response to the vibration having a large amplitude is very complex, and it is therefore hard to calculate the damping effect from the natural frequency and the damping properties.
(2) The damping properties of the porous member or the like is indefinite, and the calculation thereof is difficult.
(3) The space for installing the damping device is limited due to the size or the like of the liquid-filled tank.